Infection of chicken eggs by Salmonella (such as Salmonella Enteritidis (SE)) is one of the principal causes of Salmonella food poisoning.
When a laying hen is infected with Salmonella, the infection spreads in the body to the ovaries and oviducts, and penetrates the eggs. Consequently, the interior of an egg is already contaminated with Salmonella when it is laid. Salmonella contamination cannot be detected by external inspection, and internal contamination cannot be removed by the washing process at grading and packaging centers (the plants where chicken eggs are cleaned, graded by size and packaged).
Even when chickens are infected with Salmonella, the rate of Salmonella contamination in the eggs produced is only about 0.01–1%, but if such eggs are not exposed to sufficient heat during preparation the bacteria may survive and proliferate to the point of causing food poisoning. Lower bacterial numbers are required to cause food poisoning in people with low resistance such as infants and the sick and elderly than in healthy adults.
Measures are necessary at all stages in the production and distribution processes from farm to table in order to ensure the hygienic quality of the eggs and prevent Salmonella food poisoning. In particular, it is necessary to reduce Salmonella infection rates in chicken flocks.
Under current poultry practices, however, chicks are produced in hatcheries without any contact with their parents, and are thoroughly disinfected at each stage in order to prevent the transmission of disease from breeding stock. As a result, the chicks do not receive from their parents the beneficial intestinal flora that they need to protect them against intestinal pathogens, and are extremely vulnerable to Salmonella at juveniles. When such chicks are then raised in the normal way in the field, it requires six weeks or more for them to develop the intestinal flora that they need to protect them against Salmonella infection.
Consequently, it is thought that Salmonella infection rates in flocks are affected by Salmonella infection of juvenile chicks with immature intestinal flora, and therefore a reduction in Salmonella infection rates among chicks is necessary in order to reduce Salmonella infection rates in flocks.
A method has already been developed of effectively preventing Salmonella infection by the controlled administration of adult intestinal flora to chicks (E. Nurmi and M. Rantala, New aspects of Salmonella infection in broiler industry, Nature 241:210–211 (1973). Using this method, proliferation of Salmonella in the bodies of chicks is effectively prevented even if they are orally infected, and the high level of excretion normally seen in the field does not occur. This method is known as the Competitive Exclusion or Nurmi method.
In general, the anaerobically cultured cecal contents, mucous membrane of the gut or feces of adult birds are used to inoculate the chicks with intestinal flora. This is known as an Undefined Culture because the species and numbers of bacteria cannot be precisely identified. Products are also available in which the bacterial species and numbers in an Undefined Culture have been identified through long-term continuous culture, or in which pure bacterial cultures isolated from Undefined Cultures have been mixed together. These are known as Defined Cultures because the bacterial species and numbers have been identified. Undefined Cultures and Defined Cultures are known collectively as Competitive Exclusion Cultures (CE Cultures).
In order for such Competitive Exclusion Cultures to be used to prevent Salmonella contamination, they must be administered to the chicks in the necessary quantity as soon as possible after hatching.
Oral administration to individual chicks as in a laboratory is ideal for this purpose, but this method is too labor- and time-intensive and consequently too expensive for application in the field. Under field conditions, spraying of hatching eggs and misting of chicks are used in the hatcheries and administration through drinking water on the farm.
Unfortunately, it is difficult to administer a sufficient quantity of Competitive Exclusion Culture to chicks soon enough after hatching by these methods. In particular, it is difficult to administer the necessary quantity of Competitive Exclusion Culture in a short period of time to 0–7 day old chicks, which consume little food and water.
Under these circumstances, the inventors previously developed a probiotic composition (a live microbial feed supplement) suitable for administering the necessary quantity of Competitive Exclusion Culture to chicks as soon as possible after hatching, in which the Competitive Exclusion Culture is fixed in a gel with polysaccharides which gelate in a water medium (Japanese Patent Application Laid-open No. H11-302185). Using this probiotic composition, the chicks' natural genetic program (habit) of pecking and ingesting solid matter in front of them is exploited to induce them to ingest the necessary quantity of Competitive Exclusion Culture in a short period of time during the first 7 days of life when they consume little food or water, and thus to protect them against Salmonella contamination.
However, a feeding apparatus and feeding method have yet to be developed capable of inducing chicks in a chick box to efficiently ingest a probiotic composition in solid gel form.